Just throwing this out there. I was working on my radio today and when I took off the radio bezel, it separated from the vents.
I had to melt it back to the bezel with a soldering iron and also super glued it just to make it stronger.
I noticed that one of the fins in my vent had come unsnapped from the bar that they all snap to. I was able to snap it back in place, but that one fin could be what's blocking your air-flow.